Ditto to thismama. They have their time and place and, unfortunately, some people do misuse them. Also, alot of the convertibles that are marketed to be used from birth on are actually too big for newborns (strap slots are too high on the lowest setting for newborns).
Up in my climate, the infant carriers are a godsend in the winter. Winters here are COLD and I'm not talking "Oh, it's 25*F, we're all going to freeze to death" kind of stuff some people think is cold (that's sweater weather to us
) but 2 week long cold snaps of -40*F/C. Infant carriers are great for the winter. I love that I can take the seat inside to keep it warm and when we get ready to go out, I can get baby snug in there w/some fleece blankets over top and not have to worry about exposing him or her to the extreme cold.
Blah . . . maybe I'm just tired this AM but I get so tired of people implying that people who use infant carriers are doing so just to avoid holding/touching/interacting w/their babies. My infant carrier has been used to keep my baby safe in the car not to avoid touching my baby.